In the following description, the term “yarn” is intended to also include the threads, tapes, profile tapes, fibrillated tapes and slit-film bands of various linear mass density, diameter, width and thickness. The term “bobbin” is intended to include any metallic or non-metallic tubes on which the yarn is wound to form a suitable package. The term ‘yarn’ is also used to describe yarn with multiple threads or ends that a single winder might receive.
Automatic turret type winders are used in production or take-up process of continuously advancing yarn, for example, in yarn extrusion machines or in rewinding process for making plurality of small size yarn packages from a large yarn package. In general, the turret type automatic winders are positioned side by side in the horizontal direction and stack one above the other in vertical direction. The number of winding positions is exemplary both in horizontal row and vertical row.
In automatic turret type winders, a continuously advancing yarn is generally wound on an initially empty bobbin to form a suitable yarn package. When the pre-determined package size (length/diameter/time) is achieved on a bobbin installed on one of the bobbin holders, generally known as a spindle, the continuously advancing yarn is transferred by an automatic transfer device to an empty bobbin installed on another spindle to make a new yarn package without interrupting the winding operation.
The transferring of yarn from a full bobbin to the empty bobbin will not be successful without a proper yarn grasping device that can ultimately transfer the continuously arriving yarn onto the empty bobbin. Also, if the yarn is not transferred in the first attempt, the continuously advancing yarn gets wasted until it is rethreaded.
Worse still, the continuously advancing yarn, if not controlled properly in case it fails to transfer onto the empty bobbin, may interfere with the other yarn winders on the same machine and cause the entire machinery to stop which results in a huge amount of wastage, machine downtime and economic loss. In the worst situations, some parts of the machinery may get damaged.
Many attempts have been made to provide a winding machine with a yarn grasping device for automatically transferring a continuously advancing yarn to a driven empty bobbin on which the yarn is to be wound subsequently to form a full package.
U.S. Pat. No. 3,921,923 discloses a method of automatically transferring a yarn in an automatic take-up motion of peripheral drive turret type, from a bobbin on which a yarn has been taken-up, to another unwound bobbin on which the yarn is to be wound subsequently. This invention does not describe the yarn grasping device, and furthermore, such type of described winders are normally for filament yarn and used with custom built bobbins made from paper core having limited reusability. One drawback of this invention is that it is complicated and standard bobbins cannot be used in the invention.
U.S. Pat. No. 5,228,630 relates to a turret type yarn winder in which a pair of chucks for holding bobbins are arranged on a turret disc coaxially and symmetrically to each other, and a full bobbin and an empty bobbin held on the respective chucks are alternately exchanged by the rotation of the disc so that the winding operation can be carried out without interruption. The yarn grasping device consists of an annular clamp member, a friction member provided on the base end surface of the spindle and means for engaging and disengaging annular clamp member from friction member at a predetermined phase.
One of the shortcomings of the invention disclosed in the U.S. Pat. No. 5,228,630 is that the use of springs and sliding rings and the fact that the grasp mechanism has multiple hooks, simply makes for a relatively complicated mechanism for grasping the yarn.
The European patent EP 1,525,150 relates to a device for catching a thread at the beginning of a reeling operation using a winder having at least two spindles. The device comprises a catching bushing having a catching slit arranged at the free end of the spindle and a friction pin arranged in the centre of the catching bushing. Additionally, a guiding bushing having a guiding slit is arranged such that the guiding bushing surrounds the catching bushing in radial direction and is positioned with axial distance to the catching bushing. A clamping apparatus for fixing the yarn during an automatic process of change of reels is arranged between the catching bushing and the guiding bushing.
The device and the process described in EP 1,525,150 are generally suitable for use with large diameter bobbins such as those with an inside diameter of 90 mm or so. The device is particularly unsuitable for use with small diameter bobbins. Small bobbins, with diameters of 35 mm or so, are generally used in circular looms which are typically employed for weaving slit-film tapes made from plastic material into woven plastic fabric. The invention described in EP 1,525,150 present an accommodation problem and may cause operational problem during the yarn transfer when used with a bobbin of small size.
Thus, there is need of a simple yarn grasping device capable of working with bobbins of various sizes, particularly, with small inside diameter. Further, the yarn grasping device of turret type winders should also automatically transfer various types of yarn, single and with multiple threads, with high reliability and consistency.